Federal appeals court judges appeared skeptical today about U.S. EPA's argument that it is required under the Clean Air Act to use a less stringent implementation regime for fine particulates than it is for more coarse -- and less dangerous -- particles.

The U.S. Court of Appeals for the District of Columbia Circuit is considering the legality of EPA's rules for implementation limits on air pollution from power plants, boilers and car tailpipes.

EPA is considering new standards for fine particulate matter, or PM 2.5, but the case before the court focuses on implementation of the existing standard.

At least one judge, David Tatel, was highly skeptical of EPA's argument, saying it made little sense that the agency is stricter about enforcing the coarse particulate matter standard even though fine particulate matter is a greater public health concern.

"I don't see why it makes much sense to separate out the fine particles," Tatel said. "I don't understand why the agency would do this."

The Natural Resources Defense Council and Sierra Club say states have too much flexibility, which means that in some cases standards are not being met. They challenged two rules, one from 2007 and one from 2008 that laid out how fine particle standards last set in 1997 should be implemented.

The environmental groups argue that EPA ignored language in the Clean Air Act as amended in 1990, which stated that particulate matter implementation is addressed in a different section of the statute than implementation requirements for other types of pollution.

The language in the statute specifically dealing with particulate matter is stricter and gives states less leeway.

EPA counters that the Clean Air Act language raised by the environmental groups applies only to implementation of standards for coarse particles, otherwise known as PM 10. The agency also maintains that it is too late for courts to consider a challenge, arguing that the petitioners are "a decade too late."

The three-judge panel did not seem interested in the latter argument. Tatel focused, laserlike, on the statutory language in the Clean Air Act, testing Justice Department attorney Brian Lynk with a constant stream of questions.

Tatel indicated he did not believe the Clean Air Act required EPA to handle fine particulate matter differently than the coarser pollutants. References in the statute to PM 10 seemed to indicate Congress was referring to particulate matter in general, which would include PM 2.5, Tatel said.

That was the argument made by Paul Cort of Earthjustice, who repeatedly made the point that PM 2.5 -- particles smaller than 2.5 microns in diameter -- are included in the statutory definition of PM 10.

Of the other two judges, only Stephen Williams spoke. He was less vociferous than Tatel but did press Lynk on the government's position. At one point, he asked whether EPA could have "singled out" fine particulate matter by revising the PM 10 standard instead of creating a new standard for PM 2.5. Then, implementation of the PM 2.5 standard would have been treated the same way as PM 10.

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